1. Field of the Invention
This invention relates to a process for preparing parabenzoquinones.
2. Description of the Prior Art
The process which has hitherto been employed for preparing parabenzoquinones by oxidizing alkylphenols includes an oxidization using salcomine [bis(salcylidene)-ethylene-diimino cobalt complex (II)] [Rec. Trav. Chim., vol 86, pp 520 (1967)]. This conventional complex exhibits a low activity for the conversion of phenols to quinones, but the most unfavorable disadvantage of the cobalt complex (II) in industrial use is that a large amount of polymers such as polyphenylether and the like are by-produced during oxidization (as is common in a direct liquid phase oxidization of alkylphenols with air in the presence of a catalyst) and, therefore, recovery of the catalyst is impossible due to the presence of these polymers. Further, the cobalt complex (II) is of poor solubility and the formation of polymers increases when the oxidization is carried out at a sufficiently high temperature to dissolve the cobalt complex (II) in a solvent. Moreover, the cobalt complex (II) lacks selectivity so that oxidization is conducted even on an alkylphenol having an alkyl substituent at the para-position as well as well as other alkylphenols.
In the light of the disadvantages described above, the process using the cobalt complex (II) has been recognized as unsuitable for industrial use for the production of parabenzoquinones.